1. Field of the Invention
This invention relates to a mechanism for sensing the distance between two relatively movable vehicle parts, such as the car body and truck of a railroad car, whose relative position is related to the load on the vehicle. An empty/load valve, actuated in response to the load sensed, controls the braking force applied to the vehicle wheels.
2. Description of Related Art
Brake cylinder force modification devices called empty/load valves are well known in the art of railway equipment engineering. See, for example, U.S. Pat. Nos. 4,648,661; 4,826,259; 4,844,554; and 4,824,179. In general, empty/load valves are actuated by movement of a sensing arm that is responsive to movement of a sprung part of a railroad car toward or away from the car wheels depending on the load on the car. A valve or valves is controlled by the sensing arm for diverting air to a storage tank or canister when the load on the car is light, i.e. when the car is empty or lightly loaded. The position of the sensing arm, and hence of a reciprocably movable rod linked to the sensing arm which operates a valve for controlling braking pressure, is determined by the load on the car.
In the past, empty/load sensor devices have been mounted beneath the bottom member of the side sill of the railroad car body. A sensing or measuring arm, or some other kind of trigger member, extended downward from the body of the prior art device to an area of contact with the side frame of a truck in order to sense the relative position of the car's body and the truck to determine the load condition of the car. Such an arrangement is suited to older railroad car designs, which provide ample room for mounting the empty/load sensing device between the bottom of the side sill flange of the car and the top of the truck side frame, even when the car is in fully loaded condition.
The older railroad cars, which provided adequate space for such under-the-sill mounting of an empty/load device, had relatively high centers of gravity compared to new car designs. Attempts to lower the center of gravity of railroad cars, motivated by safety and other considerations, have resulted in a significant reduction of the distance, under fully loaded conditions, between the car side sill flange and the truck frame member. Instead of the conventional five to seven inch separation found in older railroad cars, modern cars can have a space between the sill flange and the opposed frame member as small as one inch or less under full load conditions. This limited space is not large enough to accommodate the conventional mounting of an empty/load sensing device. There are also practical restrictions as to where the empty/load mechanism can be located on the car body if it is to work effectively.
The empty/load sensor mechanism of the present invention can be advantageously employed for modern railroad cars that impose space restraints that are considerably more severe than those of the prior art.